Multiple wheel tire with reduced noise

ABSTRACT

The present invention discloses a vehicle tire, which radiates low external tire/road rolling noise and comprises a rim (1) to the periphery of which a multiplicity of in axial direction separated sub-tires (5) are attached, each of which has an outer diameter/sectional width ratio (2r/b), which is greater than 8. These individual sub-tires are, for further improved noise characteristics, entirely filled with soft rubber or a soft plastic material.

BACKGROUND

The present invention concerns a vehicle tire with reduced rolling noiseemission and a method for its manufacture.

A considerable environmental problem in today's society is noiseemission from roads and streets. At lower speeds and high acceleration,the noise from the power unit dominates at the receiver point in mostcases compared to the rolling noise.

At speeds exceeding 50 km/h, however, rolling noise created by the tirecontact with the road will dominate. This means that a great portion ofthe noise problems that exist along streets and roads even in urbanareas are caused by tire/road noise. For those areas it would not helpmuch to further reduce the noise emission from the power units. The factthat the tire/road rolling noise dominates the total noise emission formost conditions at speeds exceeding 50 km/h contributes to a certainunderstandable disinclination of car manufacturers to further reduce thenoise emission from the power unit. A reduction of the tire/road rollingnoise would thus contribute directly to solve noise problems at streetsand highways where speed is higher than 50 km/h and also contribute to ageneral reduction of the road traffic noise at lower speeds, as reducedrolling noise would increase motivation also for power unit noisereduction. There are mainly three known methods up to now on how toreduce tire/road rolling noise.

1. Changing the tread pattern. The length of different tread blocks isvaried in the direction of rotation so that the tonal components of thenoise emission is spread around the mean frequency.

2. Changing the rubber compound so that higher compliance is obtained.

3. Influencing the texture of the road surface to obtain an optimaltexture depth with respect to noise.

The first method can probably not give any further noise reductionbecause of an already well developed technique. The tonal contributionto the total noise emission is less dominating for coarse road surfaces,as the random road surface excitation of the tire would dominate noiseemission in these cases. The second method cannot be used without someincrease of tire wear. It gives noise reduction but is not acceptablefrom an economical point of view.

In co-pending application PCT/SE79/00152 is disclosed a vehicle tire,which radiates little external noise. This has been achieved amongothers by the tire having an outer diameter/sectional width ratio whichis greater than 8. For a further reduction of the radiated noise thetire is also totally or partially filled with soft rubber or the like.

In certain cases though it might be difficult to find a tire whichfulfills the desired outer diameter/sectional width ratio without itsbearing capability and/or its contact surface being decreased.

The object of the present invention is to disclose a vehicle tire which,while maintaining the desired bearing capability and/or contact surfaceto the road, yet radiates little external noise.

According to the present invention this has been achieved by mountingseveral individual tires on a rim of a suitable dimension, each tirehaving an outer diameter/sectional width ratio greater than 8. The tirescan be filled with only compressed air or soft rubber (or the like) oronly partially with soft rubber and the remaining part of the cavitywith compressed air.

A conventional tire must have a so called "crown-radius", i.e. the tiretread has a certain curvature perpendicular to the tire rotationdirection. This means that the tire has a larger gross diameter in themiddle of the tread compared to the gross diameter at the edges orshoulders of the tread surface. The reason for this is that the middleof the tread surface should have essentially the same contact pressurecompared to the edges and shoulders of the tread surface. Thus, themiddle portion of the tread surface must be pressed in towards the wheelcenter at contact with the road surface during the rolling of the tireand thereafter, when the tread rubber leaves the road contact,elastically spring back to its original form. These deflections, andespecially the "snap"-deflection at the tread release, contribute to agreat extent to the generated external noise. Through the fact that thepartial-tires according to the invention are so narrow, they can be madewith an essentially plane tread surface (seen in cross section), alsoallowing the existence of some kind of tread pattern.

The invention will be further described with reference to the annexeddrawing, which shows an axial cross section through an embodiment of awheel according to the invention.

The wheel shown in the drawing consists of a main rim 1, which isprovided with a hub 2 with holes 3 for mounting on a shaft. On theperiphery of the main rim 1 several sub-rims 4 are arranged in asuitable way and with axial play. Each of the sub-rims 4 supports a tire5, which has an outer diameter/sectional width ratio (2r/b) greater than8 and which in a conventional manner could be filled with compressedair.

Already the said dimensioning of the tires involves a reduction ofradiated noise from the rolling tire. To obtain a further reduction ofthe radiated noise, the inner cavities of the tires 5 could entirely(tire 5a) or partially (tires 5b and 5c) be filled with soft rubber or asoft elastomeric or plastic (resin) material 6, which preferably shouldhave a hardness of less than 35° Shore A. In case the tires are onlypartially filled with a soft polymeric material, the remaining part ofthe cavity is filled with compressed air. In the tire 5b the soft rubbermerely fills the outer parts (in a radial direction) of the cavity whilein tire 5c the rubber material also extends along the inside of the tireside-walls up to the tire foot 7. The tread surfaces 8 of the tires 5are in the shown example essentially plane in sectional view. Therebythe above-mentioned, noise generating deflection in the tread rubber isavoided.

The sub-rims 4 can be manufactured in one piece with the main rim 1,which in such a case is provided with a number of continuouscircumferential grooves corresponding to the number of tires, the edgesof which correspond to the inner surfaces of the sub-rims 4, or twice asmany continuous circumferential tire beads or protrusions between two ofwhich the tires are mounted.

The rubber or plastic filling 6 should be of a material absorbingstructureborn sound and having a high loss factor.

I claim:
 1. A vehicle wheel having low rolling noise comprising:a rimlocated about an axis of said wheel; a plurality of tires mounted onsaid rim, each of said tires having an inner cavity and being axiallyseparated from each other; each of said tires having anouter-diameter/sectional-width ratio (2r/b) of greater than 8 wherein 2ris the outer diameter of said tire and b is the cross-sectional width inthe axial direction of each individual tire; and, each of said cavitiesbeing filled with a filler material having a hardness of less than 35°Shore A (DIN 53 505).
 2. The wheel of claim 1 wherein said fillermaterial is rubber.
 3. The wheel of claim 1 wherein said filler materialis a plastic.
 4. The wheel of claim 1 or 2 or 3 wherein each of saidtires has a tread surface that is essentially plane when viewed incross-section.
 5. The wheel of claim 1, wherein each of said tires aremounted on a corresponding sub-rim member, and wherein each of saidsub-rim members are in turn mounted on said rim.
 6. A method of reducingrolling noise on a vehicle including the steps of:providing said vehiclewith wheels each having a plurality of tires mounted on a wheel rimmember thereon and each tire having a cavity therein; structuring eachof said tires so that the outer-diameter/sectional-width ratio (2r/b) isgreater than 8 wherein 2r is the outer diameter of each said tire and bis the cross-sectional width thereof in the axial direction; and fillingeach of said cavities with a filler material having a hardness of lessthan 35° Shore A (DIN 53 505).